There are many important properties in a golf ball, one of which is its flight distance. The flight distance of a golf ball is governed by various factors such as initial velocity, number of revolutions, angle of departure, moment of inertia, dimple form and the like. Among them, the most important factor is initial velocity which is particularly governed by the rebound characteristics. Therefore the rebound characteristics are very important.
There have been two types of golf balls known in the prior art. One is a wound golf ball and the other is a solid golf ball. The solid golf ball is very popular because of its cheap production cost and durability, in comparison with the conventional wound golf ball. The solid golf ball has been improved with respect to materials to be formulated and its construction to provide various types of solid golf balls having excellent properties since the golf ball was proposed by J. S. Bartsh. However, satisfactory rebound characteristics still have not been imparted to such solid golf balls.
The conventional solid golf balls are classified by their construction into one-piece solid golf balls having a unitary layer and two-piece solid golf balls produced by covering a solid core with a cover. Besides these, a multi-piece solid golf ball, in which the solid core of the above two-piece solid golf ball is plural-layered, has recently been proposed (see Japanese Patent Publication (unexamined) No. 49840/1976, Application No. 122898/1974). The solid golf ball disclosed in this publication has more weight in an inner layer than in an outer layer, which is the same construction as the conventional wound golf ball.
For improving the multi-piece solid golf ball, the present inventors have made proposals in Japanese Utility Model Application Ser. No. 64006/1983 and Japanese Patent Publication (unexamined) No. 194760/1984, in which the weight of the plural-layered solid core becomes heavier closer to the cover. This multi-piece solid golf ball effectively improves rebound characteristics without affecting adversely its other properties.
However, in such a multi-piece solid golf ball, since a filler, such as zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate and the like is formulated in a high amount, the rubber has to be formulated in a small amount, and thus the rebound characteristics become worse. Accordingly, the improvement of the rebound characteristics by this technique has its limitations.